VIEWS: 39 PAGES: 6 POSTED ON: 10/5/2010
Plasma Membrane & Cell Transport Plasma Membrane • Responsible for maintaining the cell’s homeostasis – Regulates what enters and exits the cell • selectively permeable – Barrier that separates the inside and outside of the cell Structure of the plasma membrane • Bilayer of phospholipids – Unsaturated lipids • fairly fluid structure Fluid Mosaic Model • Fluid – Constant motion – Components change • Mosaic – Different components • Phospholipids – flexible & in constant motion • Cholesterol – membrane rigidity (structure) • Membrane proteins – transport, receptor, recognition… Membrane proteins • Peripheral proteins – attached to the inner or outer surface – Hydrophilic regions • Integral proteins – In or through the membrane – Hydrophobic regions Membrane Protein Types • Receptor proteins – binding sites for molecules (hormones) – Trigger a cellular response (start or stop ____) • Recognition proteins – provide cell & self identity Membrane Protein Types • Transport proteins – use ATP – move molecules across the membrane • Channel proteins – passageway for • Hydrophilic • large molecules • No energy needed Cell Junctions • Connections that bind neighboring cells together – Physical – Communication • Animal Cell Junctions – Adhesion / Desmosomes / Anchoring – Tight – Gap • Plant Cell Junctions – Plasmodesmata (same purpose as gap junctions) Adhesion Junctions • Through the plasma membranes • Prevents separation • Cells that stretch • Skin • Heart • Gut Tight junctions • Prevents leaking – Stomach • Acid stays – Intestine lining • Nutrients diffuse through cells • Waste stays in intestine Gap Junctions • Communication channels – Holes through membrane – Links cytoplasm • Rapid communication • Cells that work in concert – Heart – Smooth Muscle Plasmodesmata • Narrow channels through cell wall – share membrane, – Share ER – Share cytoplasm • Quick communication – Response Passive Transport Osmosis & Diffusion Transport • Passive – No energy is needed – Molecules move with the concentration gradient • Active – Energy (ATP) is needed – Molecules move against the concentration gradient Osmosis Isotonic Solution • Equilibrium – Water moves equally in and out of cell. – equal concentrations of EACH dissolved particle. Hypotonic Solution • Water leaves – Water moves into the cell. (Net movement) • higher concentration of other particles inside cell Hypertonic Solution • Water enters – Water moves out of the cell. (Net movement) • higher concentration of dissolved particles outside cell. What types of solutions are these? Osmoregulation: contractile vacuole • What type of environment does it live in? Plasmolysis What are the types of Passive Transport • Diffusion – Osmosis • Facilitated Diffusion • Small molecules moving through the plasma membrane (fit between the phospholipids) • Diffusion of water • Large or medium sized polar molecules moving through the plasma membrane (need help/large openings to pass through) Electrochemical Gradient Cotransport Types of active transport • Active transport using membrane proteins • Endocytosis – Phagocytosis – Pinocytosis – Receptor-Mediated • Exocytosis Active Transport • Uses Membrane Proteins • Builds a Concentration Gradient – Stores energy – Across a membrane – Molecules – H+ (electrochemical) • Endocytosis • Exocytosis • Molecules do not pass through the membrane until released Water Potential • = p + s • = water potential • p = pressure potential • s = solute potential = -iCRT (this is a negative number) – i = ionization constant ( 1 if no ions) – C = Concentration – R = pressure constant ( 0.0831 liter bars/ mole ˚K) – T = temperature ˚K (273 + ˚C) – Water always moves from a high to low water potential/# of water molecules • Pure water @ 1atm = 0 – Increase the number of solutes, # becomes negative – Increase the pressure increases the water potential • p = 0 for animal cells since there is no cell wall Osmosis Lab 1D: What is the water potential of potato cells? • = p + s • p = 0 (always assume zero unless given) • s = -iCRT = » -(ions)(concentration)(0.0831 liter bars/mole K) (295 K) • = 0 + -(1)(C)(0.0831 liter bars/mole K) (295 K) Questions 1D • If a potato core is allowed to dehydrate by sitting in the open air, would the water potential of the potato cells decrease or increase? Why? – Hint: solute concentration • If a plant cell has a lower potential than its surrounding environment and if pressure is equal to zero, is the cell hypertonic or hypotonic to its environment? Will the cell gain water or lose water? Explain
"Plasma Membrane Cell Transport Plasma Membrane Cell Transport Plasma Membrane • Responsible"